On Sat, 22 May 2004 21:04:20 -0700, jizhonghe wrote:

Great. Thanks for the clarificaiton. I always thought they just give you a
low number. Now I know at least they are honest albeit misleading. So I
looked up the C152 POH and the CAS stall clean is actually 47kts (54mph).
I should re-adjust my goal. I think a CAS of 40mph should be quite
respectable for a little bush plane. And the square of (54/40)^2=1.83 with
the light weight should be able to reduce the T/O run by half.


The stall speed basically depends on the wing loading and the maximum
coefficient of lift that is achieved.

The stall speed in equivalent airspeed (which can be considered to be the
same as calibrated airspeed for low speed and low altitude) is:

VS = 0.8379 * sqrt(wing loading/CLmax)

VS is in knots,
Wing loading is in lb/sq. ft

I don't have data for the C150 at hand, but looking at the C182Q POH for
an example, I get wing loading of 2950/174 = 16.95 lb/sq ft. The forward
CG stall speed at 2950 lb is 54 kt CAS. This requires a CLmax of 1.72,
which is about what I would expect for a flapped wing with no leading edge
devices.

Several references indicate a well designed slat might give about an extra
1.0 CLmax, so you might be able to get the C182 CLmax to about 2.7. This
would give a stall speed of about 43 kt CAS, or about 80% of the original
value. You think you can get the C150 stall speed from 54 mph to 40 mph,
which would be a reduction to 74% of the original value. This seems
unlikely from just adding slats. You would need to also make a big
improvement to the flaps. These mods add weight, and they would require a
lot of knowledge of aerodynamics and structural engineering to actually
achieve the predicted performance, and to have a strong structure.

References:

Fluid Dynamic Lift, Hoerner
Theory of Wing Sections, Abbott and Doenhoff

Good luck.